Mobspawner will instantly spam the scoreboard team list if it 'Delay' tag is in use, e.g. set to 0 even if mobs are not spawning, and will not reset until I empty the team list. This is a major problem as eventually, if left alone, it will cause the team list to reach numbers in the thousands, which then causes players to be unable to connect due to "Badly compressed packets" error

Can be reproduced via creating a team ("WorldTSA" for this example) dropping a command block and activating with

/setblock ~ ~1 ~ minecraft:mob_spawner 0 replace {Delay:0,SpawnData:{id:"minecraft:vex",Team:"WorldTSA"}}

It only needs to be placed down, it happens even before any mob actually spawns. If you've placed the spawner for more than 5 seconds I do not recommend "/scoreboard teams list" because it will disconnect you from game. You can see the number using "/scoreboard teams empty" instead